1. Field of the Invention
The present invention relates to a marine vessel propulsion structure and marine vessel driving apparatus which causes a marine vessel to be propelled using a plurality of propellers.
2. Description of the Related Art
Hitherto, in order to facilitate improving of maneuverability of a marine vessel such as a boat or the like upon steering of the marine vessel, two so-called outboard drives or inboard-outboard drives which are each provided with a single engine and propellers driven by the single engine are installed at predetermined locations of a rear portion of the marine vessel.
Moreover, there is known a tandem propeller mounting structure in which two forward and rearward propellers constituting a tandem propeller system are mounted on a single propeller shaft (for example, Japanese Patent Application Laid-Open No. Hei. 5-58389).
Also, there is known a structure in which a plurality of screws are mounted on a single shaft (for example, Japanese Utility Model Application Laid-Open No. Sho. 58-40498).
In a case where, like the conventional marine vessel, a marine vessel is provided with two outboard drives or the like, there are raised problems that much fuel is consumed for driving two engines and fuel economy is therefore poor, a poor balance of the marine vessel is offered due to an increased weight of the rear portion of the marine vessel, and maintenance cost of the marine vessel is increased.
Furthermore, in a marine vessel employing the structure in which the plurality of propellers are mounted on the single propeller shaft like the above-mentioned prior art structure, turning-around of the marine vessel is performed with resort to a rudder, so that it is hard to delicately steer the marine vessel. For example, in a case where an advancing direction of the marine vessel is controlled in a narrow harbor or the like, a high-level steering technique is required.